Clean rooms found in manufacturing, research, and other facilities are typically classified into two broad categories based on the static air pressure inside the rooms relative to atmospheric pressure and/or based on the air pressure in spaces adjacent the clean rooms. A positive air pressure room is maintained at an absolute air pressure greater than atmospheric pressure, greater than the air pressure in spaces adjacent the clean room, or both. The positive air pressure in such rooms is provided by pumping filtered and/or conditioned air into the rooms and controlling the flow of air out of the rooms. The adjacent spaces, which may be manufacturing facilities or offices, are typically maintained at or close to atmospheric pressure by heating, ventilation, and air conditioning (HVAC) systems, or by providing an opening to the environment that allows the adjacent spaces to equilibrate with atmospheric pressure. Thus, air flowing from the positive pressure clean room will flow toward the lower pressure in adjacent rooms or to the atmosphere.
When a positive air pressure clean room is breached, air flowing to adjacent spaces or the atmosphere is generally not a problem as long as airborne contaminants present in the clean room do not pose a potential adverse health effect to people in the adjacent spaces. Typically, the air inside clean rooms in which electronics, aerospace hardware, optical systems, military equipment, and defense-related research are manufactured or conducted may not contain airborne gases, vapors, and particulate matter at concentrations that present a safety or health concern to human health or the environment. However, that is not always the case, as other operations within those industries may generate contaminants that are above acceptable levels and, therefore, must be prevented from escaping the clean room without treatment.
A negative air pressure room is maintained at an absolute air pressure that is either less than atmospheric pressure, less than the air pressure in spaces adjacent the clean room, or both. The negative pressure is maintained by pumping air out of the room at a rate faster than that at which filtered and/or conditioned air is pumped into the room. Negative pressure rooms are often used when there is a concern that contaminants in the air in the room may pose a potential health threat to human health in adjacent spaces or the environment.
Notwithstanding the human health and environmental implications, certain types of manufacturing and research operations must be conducted within a positive air pressure clean room to satisfy regulatory requirements and industry-adopted good manufacturing and laboratory quality control standards. For example, state and federal regulations, including those promulgated by the National Institute for Occupational Safety and Health (NIOSH), may necessitate the use of positive or negative pressure clean rooms.
In particular, the U.S. Food & Drug Administration (FDA) requires that pharmaceutical production be done within the confines of clean rooms that provide for the validation and certification that manufactured batches of pharmaceutical products are being produced in a sanitary environment.
Positive and negative air pressure clean rooms have been used for many years. U.S. Pat. No. 4,604,111, for example, discloses a negative pressure apparatus and method for protecting the environment and populations from airborne asbestos and other particulate contamination inside a building, which includes an enclosure having a blower to pull air into a filtration unit inside the enclosure and dispel the filtered air to the atmosphere. U.S. Pat. No. 5,645,480 discloses the general features of a clean room.
Various FDA regulations and standards also specify requirements for air sampling and/or air monitoring equipment to be used inside clean rooms to verify or validate the cleanliness of the facility during certain drug manufacturing activities. The regulations also provide for electronic data recording, accuracy, precision, and record-keeping relating to monitoring the air quality within clean rooms. Similar requirements are imposed on other industries, such as the biotechnology industry.
U.S. Pat. No. 6,514,721 describes an air sampling device and method for collecting airborne pathogens and psychrometric data from a room or from remote air samples where the sample volume is electronically controlled by closely monitoring fan speed. That patent illustrates a device that draws room air into a sampling device using a pump, which causes pathogen-containing particulates in the air to impact a growth/inhibitor media (a solid, liquid, gel, or mixture thereof) stored in a dish that is positioned within the sampling device. The patent states that previous sampling devices could not achieve a constant volumetric air flow of better than +/−30% relative to a nominal or set-point flow rate, which caused a large variability in calculated concentrations of pathogens.
As U.S. Pat. No. 6,514,721 suggests, one of the keys to successfully monitoring the air quality within a clean room is to ensure that the air flow rate through the air sampling/monitoring devices is very accurately determined during the time when a volume of air is collected. That fact is also appreciated in U.S. Pat. No. 4,091,674, which discloses an electronically timed, positive displacement air sampling pump for use with a wide variety of air sample collecting devices and in a wide range of environmental conditions. The disclosed invention is said to provide accurate average flow rate, independently metered total volume, operating time register, and audible “rate fault” alarm. In that patent, accuracy is achieved by using a timing circuit coupled with a mechanical bellows.
U.S. Pat. No. 6,216,548 illustrates a control system flow chart for an air sampling device for use in a controlled environment. In particular, the patent discloses a controller logic that involves turning on a pump, checking pressure, monitoring sampling time, drawing air into the sampler, shutting off the pump, and checking for leaks in the lines. The patent also teaches using a purge system for purging the lines and associated air particulate sampler using a purge gas such as nitrogen gas. In that patent, air sampling only occurs at one location (e.g., a processing chamber for semiconductor devices).